Industrial sewing machines of conventional, hands-off, sewing head type make, generally define a supporting base from which frontwardly projects a much narrower main cylinder bed. The cylinder bed is narrow, for reducing weight and storage volume. The top, planar work surface of the free end of the cylinder bed comprises a throat plate and a slide cover plate, underlying the reciprocatable needle bar and presser bar carried by the sewing head.
It has long been recognized in the art that, for carrying out fabric sewing operations in an efficient fashion, the top, work supporting surface of the narrow cylinder bed should be temporarily enlarged, so as to address the difficulties in the handling of flat work pieces, particularly those of large size. This is why auxiliary bed plate extension members have been provided: see for instance Gegauf U.S. Pat. No. 2424025; Kasahara et al U.S. Pat. No. 4114548: McGann U.S. Pat. No. 4565142.
In this latter U.S. Pat. No. 142', the cylinder bed extension 30 is of U-shape, providing a planar, upper work surface 32, and defining a central recess 33 shaped to conform to the cylinder bed work supporting surface 15. The planar, work-supporting surface 32 of the U-shape bed extension extends coplanar with the work supporting surface 15 of the cylinder bed 13, so that both surfaces may serve as an enlarged, common work supporting surface.
These U-shaped bed extensions have been plagued by problems in the past. First, locking of the bed extension to the sewing machine was not totally secure, due to low resistance to dislodgement in view of the known usual forces applied during work manipulation during sewing. Also, because the dimensions of sewing machine beds usually differ for different manufacturers, as will the dimensions which may be selected for web thicknesses, flange widths, etc. . ., in the bed extension, a variety of bed extensions of different sizes must be acquired and stored by companies in the garment manufacturing business, whenever--as is usually the case --more than one make of sewing machines are used. The reasons why cylinder beds of different sewing machine manufacturers are of different sizes, may have to do with these manufacturer's concern that parts from one competitor could undesirably be acquired by a user to fit their own sewing machine. That is to say, different standards in size promote customer brand loyalty. This is not in the interest of the customer-user of the sewing machines.